Polymethylmethacrylate (PMMA) has been used in anterior and posterior stabilization of the spine for metastatic disease, as described by Sundaresan et al., "Treatment of neoplastic epidural cord compression by vertebral body resection and stabilization." J Neurosurg 1985;63:676-684; Harrington, "Anterior decompression and stabilization of the spine as a treatment for vertebral collapse and spinal cord compression from metastatic malignancy." Clinical Orthodpaedics and Related Research 1988;233:177-197; and Cybulski, "Methods of surgical stabilization for metastatic disease of the spine." Neurosurgery 1989;25:240-252.
Deramond et al., "Percutaneous vertebroplasty with methyl-methacrylate: technique, method, results [abstract]." Radiology 1990;117 (suppl):352; among others, have described the percutaneous injection of PMMA into vertebral compression fractures by the transpedicular or paravertebral approach under CT and/or fluoroscopic guidance. Percutaneous vertebroplasty is desirable from the standpoint that it is minimally invasive, compared to the alternative of surgically exposing the hard tissue site to be supplemented with PMMA or other filler.
The general procedure for performing percutaneous vertebroplasty includes the percutaneous injection of PMMA or other bone implant material into the damaged or fractured bone tissue of a vertebra. During injection of the bone implant material, fluoroscopic imaging or another imaging technique is used to track the path that the bone implant material takes as well as its final position upon implantation. Contrast agents such as barium sulfate powder are often used to aid the visibility of the bone implant material by imaging. However, the barium sulfate powders and other contrast agents presently used are generally very fine. This type of contrast agent is fairly effective once a given mass of the mixture of it with the bone implant material has accumulated at an implant site. However, for purposes of tracking the flow and leading edge surfaces of a bone implant material during injection, or for viewing small volumes of the implant material, the contrast agents presently used are inadequate.
This inadequacy becomes especially important during injection of liquid or flowable bone implant materials, as is the case with percutaneous vertebroplasty, since viewing of the path taken by the implant material is very important. That is because the bone implant material may take a path where it begins to enter the venous system, where it is not only unwanted, but where it could have very damaging effects. Thus, an improvement in the visibility of bone implant materials during injection is needed.
The use of radiographic contrast agents in a three dimensional, solid conglomerate of polymer particles which is used as a starting material for the preparation of bone cement is disclosed by Darkener in U.S. Pat. No. 5,574,075. The agents may be particulate, having a size range of between 5 and 300 .mu.m. Darkener makes the three-dimensional conglomerate of polymeric particles, with the idea of converting the powder phase of the precursors of a PMMA bone cement mixture into a solid phase, similar to cube sugar.
Cooke et al., in U.S. Pat. No. 5,476,880, discloses the incorporation of sized, radiopaque particles into a PMMA bone composition that is additionally reinforced with previously sized reinforcing fibers. The preferred radiopaque agent is zirconium dioxide, which may be present at a level between 1-15% by weight of the powder. Barium sulfate may also be used. The radiopaque powder preferably has a diameter of about 1.mu..
Accordingly, there exists a need for a more visible composition to enable the tracking of the path of implantation taken by an implant able bone composition, particularly flowable or liquid compositions which are implanted from a remote site, by injection or other means.